1. Field of the Invention
The present invention relates to a friction stir welding method and an apparatus by which a conductive material, such as aluminum (including aluminum alloy) or the like, and other magnetic materials are welded by friction stir welding (hereinafter friction stir welding is referred to as “FSW”).
2. Description of Related Art
In every case of a conventional FSW method, frictional heat is made use of by a FSW tool comprising a probe and a shoulder portion. The probe is inserted into a weld portion to be welded by FSW and the shoulder portion is urged against members to be welded, such as metal members, (hereinafter referred to as “weld object members”), while the FSW tool is rotated. For this reason, the FSW tool is needed to have a strong rigidity so as to withstand the urging force. Also, a large amount of power is needed so that the FSW tool is forcibly rotated so as to maintain the friction.
Moreover, with respect to the weld object members, a reinforcing means is needed in order for the weld object members to be supported against the urging force of the FSW tool.
Also, in order to obtain a desired frictional heat, a diameter of the probe is sometimes needed to be made larger than a size needed for stirring the weld object members. If weld object members, such as hollow members, have a bone member therein for reinforcement under the weld portion, there is a restriction that a thickness of the bone member must be made larger than the diameter of the probe. That is, there is a problem that the bone member must be selected corresponding to the diameter of the probe.
Likewise, if an integrated piping plate is to be manufactured by FSW, since the distance between adjacent fluid passage grooves of the integrated piping plate cannot be smaller than the diameter of the probe, the degree of the integration is restricted by the diameter of the probe.
Also, there is a restriction of the welding speed due to the welding speed being decided by the time needed for sufficient frictional heat to be generated by the FSW tool.
Also, there is a conventional FSW method in which an additional heating source other than the frictional heat generated by the FSW tool is provided at and around the weld portion to thereby enhance the welding speed. For example, as shown by perspective views of FIGS. 10, 11 and 12, a rotating probe 53 is inserted into a weld portion 54 between weld object members 50, 51, both made of aluminum, and a contact portion of the weld object members 50, 51 making contact with the probe 53 is softened by the frictional heat and stirred by the probe 53. In this state, a FSW tool 52 together with the probe 53 is moved along the weld portion 54 so that the weld object members 50, 51 are welded together, wherein a front portion of the weld portion 54 in a moving direction X of the probe 53 is heated by an outside heating source (laser beam 55 in FIG. 10, gas flame 56 in FIG. 11 and a heating roller 57 in FIG. 12) so that the temperature there becomes 100 to 300° C. This is proposed in Patent Document 1 mentioned below.
Also, as shown by a perspective view of FIG. 13, a heating device comprises an FSW tool having a probe 53 that moves on a weld portion 54 of weld object members 50, 51. Induction heating sources 58, 59 are arranged at front and rear positions of the probe 53 so as to move together with the probe 53. A power source 60 is used for supplying the induction heating sources 58, 59 with electric power and a temperature setting means 61 is used for setting a temperature of the weld portion 54. A gap is provided between the induction heating sources 58, 59 and the weld object members 50, 51. At the time of welding, the induction heating sources 58, 59 are heated by the power source 60 to a set temperature set by the temperature setting means 61, so that front and rear portions of the weld portion 54 in the moving direction X of the probe 53 are heated by the induction heating sources 58, 59. This is proposed in Patent Document 2 mentioned next.                (Patent Document 1) Japanese published patent 3081808 (FIGS. 1, 2 and 3)        (Patent Document 2) Japanese laid-open patent application 2003-94175 (FIG. 1)        
Nevertheless, the methods of the above-mentioned Patent Documents 1 and 2 are only provided to show that the pre-heating is done for shortening the treatment time of the FSW method and that post heating is done for enhancing the quality after the treatment. The methods of Documents 1 and 2 have several disadvantages. Specifically, the places to be heated are distant from the place where the FSW is being carried out, thus making it difficult to effectively control the degree of heating and softening of the place where the FSW is being carried out. Also, a large amount of power (electric power) is needed for driving the FSW tool, and a larger FSW tool than is necessary must be used.